Miniature low-vibration active cooling system with conical rotary compressor

ABSTRACT

A system for cryocooling an optical sensor on a satellite to a temperature below 200K with minimal vibration comprising a miniature conical rotary screw compressor comprising an inner element configured to only rotate around a first stationary axis and an outer element configured to only rotate around a second stationary axis so that both elements revolve with minimal vibration; with at least one of a) a length of at least one of the inner element and the outer element is between 10 mm and 100 mm; b) a diameter of at least one of the inner element and the outer element is between 2 mm and 45 mm; c) a compression ratio of the rotary screw compressor is between 1:2 and 1:20; and d) a shaft speed of the conical rotary screw compressor is between 1001 and 20000 revolutions per minute.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part patent application of U.S.application Ser. No. 14/837,736 entitled “Miniature Low-Vibration ActiveCooling System with Conical Rotary Compressor,” filed on Aug. 27, 2015,which is incorporated herein by reference.

FIELD

The present disclosure relates to the use of a miniature activecryocooling system for use on a satellite, the cryocooling systemcomprising a miniature conical rotary compressor with a high compressionratio and which operates with minimal vibration.

BACKGROUND

Heat removal and temperature control has become a highly important issuewith CubeSats (100 mm×100 mm×100 mm−scale) and small satellite platforms(1 m×1 m×1 m−scale). A significant use of such satellites includes Earthobservation using optical sensors. With increasing power budgets onCubeSats, increasing radio power requirements, and higher data rates,optical sensors experience more heat, Signal-to-noise ratio (SNR)decreases, and the quality of observation is reduced. Thus, efficientcooling systems for satellite optical sensors are required. The tasksfor such a system include moving tens of watts away from a heat sourceand cooling to cryogenic temperatures below 123K (−150° C. or −238° F.)in order to enhance the SNR of the optical sensors. Excess heat may beradiated into Space by radiation from black panels according toStefan-Boltzmann law. However, prior art cooling systems encounterseveral technical problems include size constraints and vibrationissues, and lack necessary efficiencies.

A first technical problem of creating a miniature cryocooling system forsmall satellites is that it must be very small. That is, they must beless than about 100 mm long and have a height of less than about 40 mm,in order to fit into 100 mm frame of a CubeSat.

A second technical problem is that compressors in such miniature coolingsystem must produce as little vibration as possible, because vibrationdistorts the image of the optical sensors on small satellites.

A third technical problem is that the miniature cooling system must bevery efficient, and not use more energy than it removes, because verylittle energy (e.g., from solar panels) is available for the coolingsystems of small satellites, and as much of the available energy aspossible is required to perform other useful functions of the satellite.

A traditional approach for cooling systems for satellites is passivecooling. Passive cooling systems consisting of heat sinks have proven tobe effective in a range of approximately 258 K to 313 K for sunsynchronous orbits. More sophisticated passive cooling systems withethane circulation between the cold and hot radiators such as thethermal control system designed for the PRISMA satellite of AgenziaSpaziale Italiana is capable of removing about 4.8 W of heat and coolingto around 185K (−88° C. or −127° F.). However, the temperature of 185Kis above the cryocooling range (e.g. below 123K), and therefore does notmeet the requirement.

Thus, active systems with a compressor can be significantly moreeffective, because the compressor heats the refrigerant throughcompression and enhances radiation of heat through black panels.Specifically, the Stefan-Boltzmann law states that while the totalenergy radiated per unit surface area of a black body is linearlydependent on the surface area of the radiating panels, it depends on thefourth power of the black panels' thermodynamic temperature T. Forexample, an active system developed by Lockheed Martin demonstratedremoval of 0.65 W and cooling to 150K, but nonetheless, still does notreach the cryocooling range of below 123K and does not remove the tensof watts needed for cryocooling, and therefore does not meet the notedrequirements.

Active cryocooling systems such as those based on reciprocatingcompressors or Stirling engines do come closer to or meet cryocoolingranges, but they also produce too much vibration due to two pistonsconstantly moving in reciprocating motion, and because of this, suchsystems do not meet the noted requirements. An example of such aminiature cryogenic cooling system is disclosed in U.S. Pat. No.4,479,358.

Other prior art such as Joule-Thomson cryocoolers are too large andheavy for small satellites. Examples of these include the 4.3 kg Oxfordcryocooler employed on UARS. These systems do not meet the notedrequirements.

Miniature twin-screw or turbo compressors can solve the technicalproblem of vibration because they operate with rotary motion and produceminimal vibration. But it is well-known that in miniature sizes, withlengths shorter than 100 mm and heights lower than 40 mm, oil-freetwin-screw and turbo compressors do not provide high compression ratiosover 1:1.5, and therefore the temperature of refrigerant does notsignificantly increase through compression. Thus, very little heat istransferred to black radiation panels and radiated into space. For thisreason twin-screw or turbo compressors do not meet the notedrequirements.

As such, there is a need for a miniature rotary compressor in an activecooling system for use on a satellite that operates with minimalvibration, provides high compression ratio of 1:2 to 1:20, elevates thetemperature of a refrigerant fluid in order to effectively radiateexcess energy into Space according to Stefan-Boltzmann law, and enablesremoving tens of watts away from a heat source and cooling to cryogenictemperatures below 123K (−150° C. or −238° F.).

SUMMARY

In accordance with various aspects of the present disclosure, there isprovided a miniature active system for cryocooling of small satellites,comprising a miniature conical screw rotary compressor operating withminimal vibration, a condenser in communication with black radiationpanels, an evaporator, and charged with refrigerant appropriate for usein space. A length of the conical rotary screw compressor may be between10 mm and 100 mm. A diameter of each of the screw elements in theconical rotary screw compressor may be between 2 mm and 45 mm, so thatthere is space for housing parts to keep within the height of 40 mm. Acompression ratio of the rotary screw compressor may be between 1:2 and1:20, so that the temperature of refrigerant is significantly elevatedduring compression. A shaft speed of the rotary screw compressor may bebetween 6001 and 20000 revolutions per minute.

In accordance with various aspects of the present disclosure, a methodof cooling an object, comprises using a cooling system to cool theobject, the cooling system comprising the steps of: removing heat fromat least one component of the object into an evaporator, thereby heatinga refrigerant in an evaporator; passing a refrigerant from theevaporator into a conical rotary screw compressor, wherein the rotaryscrew compressor includes an inner element and an outer element; amotor; a condenser; an expander; and the evaporator; compressing therefrigerant in the conical rotary screw compressor, thereby heating therefrigerant; passing heated refrigerant from the conical rotary screwcompressor to the condenser; passing heat from the condenser into atleast one cooling panel; and radiating heat from the at least onecooling panel. In accordance with various embodiments using the methodinclude at least one of: a) a length of the conical rotary screwcompressor is between 10 mm and 100 mm; b) a diameter of each of thescrew elements of the conical rotary screw compressor is between 2 mmand 45 mm; c) a compression ratio of the conical rotary screw compressoris between 1:2 and 1:20; and d) a shaft speed of the conical rotaryscrew compressor is between 6001 and 20000 revolutions per minute;

Any aspect of the present disclosure may be applied to other aspects ofthe disclosure, in any appropriate combination. For example, apparatusfeatures may be applied to method features and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this specification, illustrate embodiments of the disclosure,and together with the description serve to explain the principles of thedisclosure, wherein like numerals denote like elements and wherein:

FIG. 1 shows a comparison of the miniature rotary conical compressor forsatellite cooling with a credit card;

FIG. 2 shows a miniature conical rotary compressor for satellite coolingheld in an adult human hand;

FIG. 3 is a cooling system for satellite equipment based on the conicalrotary compressor;

FIG. 4 shows a CAD model of the inner conical screw rotor and the outerconical screw rotor of the conical rotary compressor;

FIG. 5 is schematic diagram of a conical rotary compressor;

FIG. 6 shows a top view of a conical rotary compressor; and

FIG. 7 shows a rotary screw compressor directly driven by an electricmotor connected through a coupling.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Persons skilled in the art will readily appreciate that various aspectsof the present disclosure can be realized by any number of methods andsystems configured to perform the intended functions. Stateddifferently, other methods and systems can be incorporated herein toperform the intended functions. It should be noted that the accompanyingdrawing figures referred to herein are not all drawn to scale, but canbe exaggerated to illustrate various aspects of the present disclosure,and in that regard, the drawing figures should not be construed aslimiting.

In accordance with various aspects of the present disclosure, aminiature rotary compressor for use in an active cooling system forobjects such as CubeSat satellites is provided. The use of aminiaturized rotary compressor can provide for a high compression ratiowith low associated vibrational effects, and may provide forsignificantly improved cooling or cooling efficiency. FIGS. 1 and 2illustrate a comparison of a miniature rotary conical compressor forsatellite cooling with a credit card and in an adult human hand. Inaccordance with various aspects of the present disclosure, a miniaturerotary compressor operates with minimal vibration, provides highcompression ratio of 1:2 to 1:20, elevates the temperature of arefrigerant fluid in order to effectively radiate excess energy intoSpace according to Stefan-Boltzmann law, and enables removing tens ofwatts away from a heat source and cooling to cryogenic temperaturesbelow 123K (−150° C. or −238° F.).

In accordance with various aspects of the present disclosure, an activecryocooling system to cool the objects of a satellite is provided. Withreference now to FIG. 3, a cooling system 70 in accordance with thepresent disclosure may comprise a miniature conical rotary screwcompressor 80, a motor 81, a condenser 84, an expander 86 and anevaporator 88. An exemplary conical rotary screw compressor and variouscomponents thereof are disclosed in PCT Patent Application No.PCT/GB/2015/050459, which is hereby incorporated by reference.Additionally, with reference now to FIGS. 2 and 3, a miniature rotaryscrew compressor 80 comprises an inner element 91 and an outer element92. In accordance with various aspects of the present disclosure, alength of at least one of the inner element 91 and the outer element 92may be between about 10 mm and about 100 mm and a diameter of at leastone of the inner element 91 and the outer element 92 may be betweenabout 2 mm and about 45 mm. Additionally, in accordance with variousaspects, a compression ratio of the rotary screw compressor 80 may bebetween about 1:2 and about 1:20. A shaft speed of the rotary screwcompressor 80 may be between about 1001 and about 20000 revolutions perminute. In various embodiments, the object being cooled may comprise asatellite.

In accordance with various aspects of the present disclosure, thecooling system may be used to cool an object and may comprise removingheat from at least one component of the object into the evaporator 88,thereby heating a refrigerant in the evaporator; passing refrigerantfrom the evaporator 88 into the conical rotary screw compressor 80;compressing the refrigerant in the conical rotary screw compressor 80,thereby heating the refrigerant; passing heated refrigerant from theconical rotary screw compressor 80 to the condenser 84; passing heatfrom the condenser 84 into at least one cooling panel 82; and radiatingheat from the at least one cooling panel 82. In accordance with variousembodiments, the at least one component of the object may comprise atleast one sensor 90. Radiating heat from the at least one cooling panel82 may comprise radiating the heat into space from the at least onecooling panel 82.

Cooling systems in accordance with the present disclosure such as thoseshown in FIGS. 1-6 may provide a method of cooling a sensor that maymeet the demanding constraints required of a cooling system for asatellite. By using a miniaturized rotary screw compressor (i.e., thosehaving the dimensions noted above), vibration may be reduced and thus,to achieve acceptable performance of image sensors, it may be necessaryto cool the sensors to an appropriate temperature without compromisingthe performance of the sensors by introducing an unacceptable level ofvibration. Thus, cooling systems using a miniaturized rotary screwcompressor may in some cases be particularly appropriate for cooling asystem that requires low vibration, and may in addition be small enoughthat it may be incorporated in a small satellite such as a CubeSat orother nanosatellite. Some embodiments of the miniaturized rotary screwcompressor may also be able to provide higher compression ratios thancould previously be provided by some compressors of comparable size,allowing the cooling system to provide effective cooling even in a verysmall system.

In accordance with various embodiments of the present disclosure,cooling systems such as those disclosed herein may provide an activecooling system elevating the temperature of gas through compression andenhancing radiation of heat through black panels. In other embodiments,different cooling panels may be used, or another method of removing heatfrom the condenser may be used. In the presently described embodiment,the cooling system cools the printed circuit board or sensor 90, thoughin alternative embodiments, the cooling system may cool differentsatellite components.

The use of the miniaturized rotary screw compressor in the coolingsystem can provide for a high compression ratio with low associatedvibrational effects, and may provide for significantly improved coolingor cooling efficiency. In various embodiments and as illustrated in FIG.3, the cooling system may be configured to heat a refrigerant duringcompression and to cool the refrigerant through radiation of energythrough cooling panels 82. The cooling panels 82 may comprise blackradiation panels.

With reference now to FIGS. 4-6, the inner element 91 and the outerelement 92 of the conical rotary screw compressor may each revolvearound a respective stationary axis, which may be described as a staticor fixed axis. Each axis may remain stationary in operation. Neither ofthe elements may perform eccentric motion thereby reducing vibrations tothe minimum.

As mentioned above, in various embodiments, the conical rotary screwcompressor may be configured to compress the refrigerant, therebyheating the refrigerant. The refrigerant may comprise any of helium,krypton, methane, or a mixture thereof.

In various embodiments and with continued reference to FIGS. 4-6, alength of at least one of the inner element 91 and the outer element 92may be between about 10 mm and about 100 mm, optionally between about 10mm and about 50 mm, further optionally between about 30 mm and about 50mm.

A diameter of at least one of the inner element 91 and the outer element92 may be between about 2 mm and about 45 mm, optionally between about 2mm and about 20 mm. A diameter of at least one of the inner element 91and the outer element 92 may be less than about 45 mm, optionally lessthan about 20 mm, further optionally less than about 18 mm, furtheroptionally less than about 15 mm.

A mass of the rotary screw compressor 80 may be less than about 100 g(excluding the motor). A small compressor is suitable for use in space,due to its small footprint and low mass. The cost of delivering thecooling system into space is be dependent on its size and/or mass.

A compression ratio of the conical rotary screw compressor 80 may bebetween about 1:2 and about 1:20. The compression ratio of the rotaryscrew compressor 80 may be at least 1:1.5, optionally at least 1:2,further optionally at least 1:5. The compression ratio may be greaterthan that of some existing small compressors. A higher compression ratiomay result in greater heat removal.

A shaft speed of the conical rotary screw compressor 80 may be betweenabout 1001 and about 20000 revolutions per minute. The shaft speed ofthe rotary screw compressor 80 may be greater than 1001 revolutions perminutes, optionally greater than 8000 revolutions per minute, furtheroptionally greater than 12000 revolutions per minute, further optionallygreater than 15000 revolutions per minute. The relative rotational speedof the inner element 91 and the outer element 92 may be less than theshaft speed.

The cooling system may be configured to support removal of between about5 W and about 20 W of heat. The cooling system may be configured tosupport removal of between about 5 W and about 50 W of heat. The coolingsystem may be configured to support removal of at least 5 W of heat,optionally at least 20 W, further optionally at least 30 W.

The conical rotary screw compressor 80 may be configured for oil-freeoperation. Alternatively, oil may be used for lubrication and/or coolingof the conical rotary screw compressor 80.

In other embodiments, a different compressor design may be used. Atleast one of the inner element 91 and the outer element 92 may have alength between about 10 mm and about 100 mm. The diameter of at leastone of the inner element 91 and the outer element 92 may be betweenabout 2 mm and about 45 mm. The compression ratio may be between about1:2 and about 1:20. The shaft speed may be between about 1001 and about20000 r/min.

The shape of the inner element 91 and outer element 92 of the rotaryscrew compressor may be determined, for example as part of a design ormanufacturing process, using a method such as that disclosed in PCTApplication PCT/GB2013/051497, which is hereby incorporated byreference.

The rotary screw compressor can be driven by an electric motor through agear train or a belt or a chain, such as shown on drawings FIG. 1, FIG.2, or FIG. 5, or directly driven by an electric motor connected througha coupling, as shown on FIG. 7. With specific reference to FIG. 7, aminiature rotary screw compressor 97 is illustrated comprising an innerelement 94, and an outer element 93, and a motor 96, wherein the motor96 and the inner element 94 are connected by a coupling 95.

Finally, it will be apparent to those skilled in the art that variousmodifications and variations can be made in the present disclosurewithout departing from the spirit and scope of the disclosure. Thus, itis intended that the present disclosure cover the modifications andvariations of this disclosure provided they come within the scope of theappended claims and their equivalents.

Likewise, numerous characteristics and advantages have been set forth inthe preceding description, including various alternatives together withdetails of the structure and function of the devices and/or methods. Thedisclosure is intended as illustrative only and as such is not intendedto be exhaustive. It will be evident to those skilled in the art thatvarious modifications may be made, especially in matters of structure,materials, elements, components, shape, size and arrangement of partsincluding combinations within the principles of the disclosure, to thefull extent indicated by the broad, general meaning of the terms inwhich the appended claims are expressed. To the extent that thesevarious modifications do not depart from the spirit and scope of theappended claims, they are intended to be encompassed therein.

We claim:
 1. An active cryocooling system for cooling the sensors in asatellite to a temperature below 200K with minimal vibration comprising:a miniature conical rotary screw compressor comprising an inner elementconfigured to rotate around a first stationary axis and an outer elementconfigured to rotate around a second stationary axis so that the axesare inclined to each other and both elements revolve with minimalvibration; a condenser in communication with black radiation panels; anexpansion device; an evaporator connected with sensors; a refrigerant;and wherein: a) a length of at least one of the inner element and theouter element of the rotary screw compressor is between 10 mm and 100mm; b) a diameter of at least one of the inner element and the outerelement of the rotary screw compressor is between 2 mm and 45 mm; c) acompression ratio of the rotary screw compressor is between 1:2 and1:20; and d) a shaft speed of the rotary screw compressor is between1001 and 20000 revolutions per minute; and e) the refrigerant comprisesat least one of helium, krypton, methane, and a mixture thereof.
 2. Anactive cryocooling system according to claim 1, wherein the activecryocooling system is for removing heat from at least one of asatellite, a printed circuit board, and a sensor.
 3. An activecryocooling system according to claim 1, wherein the active cryocoolingsystem is configured to heat the refrigerant during compression and tocool the refrigerant through radiation of energy through the blackradiation panels.
 4. An active cryocooling system according to claim 1,wherein the mass of the conical rotary screw compressor is less than 100g.
 5. An active cryocooling system according to claim 1, wherein acompression ratio of the conical rotary screw compressor is at least oneof: at least 1:3 and at least 1:5.
 6. An active cryocooling systemaccording to claim 1, wherein the cooling system is configured tosupport removal of between 5 W and 20 W of heat.
 7. An activecryocooling system according to claim 1, wherein the conical rotaryscrew compressor is configured for oil-free operation.
 8. An activecryocooling system according to claim 1, wherein oil is used forlubrication or cooling of the conical rotary screw compressor.
 9. Amethod for cooling the sensors in a satellite with minimal vibration,comprising the steps of: removing heat from at least one component ofthe satellite into an evaporator, thereby heating a refrigerant in theevaporator; passing a refrigerant from the evaporator into a miniatureconical rotary screw compressor; compressing the refrigerant in theminiature conical rotary compressor with minimal vibration, therebyelevating the temperature of the refrigerant; passing heated refrigerantfrom the miniature conical rotary screw compressor to the condenser;passing heat from the condenser into at least one cooling panel; andradiating heat from the at least one cooling panel. and wherein: a) alength of at least one of an inner element and an outer element of theminiature conical rotary screw compressor is between 10 mm and 100 mm;b) a diameter of at least one of the inner element and the outer elementof the miniature conical rotary screw compressor is between 2 mm and 45mm; c) a compression ratio of the miniature conical rotary screwcompressor is between 1:2 and 1:20; and d) a shaft speed of theminiature conical rotary screw compressor is between 1001 and 20000revolutions per minute.
 10. A method according to claim 9, wherein themethod for cooling the sensors is configured to heat the refrigerantduring compression and to cool the refrigerant through radiation ofenergy through cooling panels.
 11. A method according to claim 9,wherein the refrigerant comprises at least one of helium, krypton,methane, and a mixture thereof.
 12. A method according to claim 9,wherein the mass of the miniature conical rotary screw compressor isless than 100 g.
 13. A method according to claim 9, wherein acompression ratio of the miniature conical rotary screw compressor is atleast one of between 1:2 and 1:20; at least 1:3, and at least 1:5.
 14. Amethod according to claim 9, wherein the method for cooling the sensorsis removes between 5 W and 20 W of heat.
 15. A method according to claim9, wherein the conical rotary screw compressor is configured foroil-free operation.
 16. A method according to claim 9, wherein oil isused for at least one of lubrication and cooling of the miniatureconical rotary screw compressor.